Whether you are a morning type or an evening type, make sure you get your eight hours’ shut-eye in somehow and you will feel the benefits, says Phil Hammond.Are you cheating on your sleep? Over the past century, we’ve reduced the average amount of time we spend asleep from nine hours in 1910, to just over seven hours in 2007. It seems our competing demands of home, work and leisure leave little time for the pillow. But does it matter? Churchill, Stalin and Napoleon were three high achievers who claim to have survived on five hours or less and Lady Thatcher still does, having famously exposed that “sleep is for wimps”.

But if you stick those who claim to only need a few hours’ kip in a darkened sleep lab, most go under for eight hours or more. And feel a lot better for it.

So how dangerous is our sleep-deprived society? Falling asleep at the wheel accounts for 20 per cent of crashes on motorways and similar roads, which tend to be more severe because it’s hard to brake when you’re asleep. And some of the greatest catastrophes of modern times are down to “sleep-stupidity”. The oil spill of the Exxon Valdez, the Challenger space shuttle explosion, the Chernobyl and Three-Mile Island disasters all involved long shifts and sleep deprivation.

So what happens inside a body deprived of sleep? For starters, your immune system falters, making you more prone to infections and perhaps even cancer. This effect kicks in after just one night of poor sleep, but is far more of a problem in the long-term. Also, the metabolic and hormone changes of chronic sleep loss mimic those of ageing and increase the risk of diabetes, high blood pressure, obesity and memory loss.

No wonder we look so knackered when we’re sleep deprived. Cutting out coffee, nicotine and alcohol can help if you’re having trouble sleeping, as can taking regular exercise (but not immediately before sleeping unless it’s sex, which is particularly good at sending men to sleep). The good news is that it doesn’t matter when you get your kip. Lie-ins, cat naps and siestas are all excellent ideas.

Indeed, Australian psychologists have discovered that those who work late at night and loll in bed in the morning are typically more intelligent than early birds. The researchers took 400 volunteers who divided themselves into “morning types” and “evening types”. Each was then subjected to mental agility and memory tests, and the midnight-oilers came out best. Maybe we should all go to night school.

Phil Hammond is a GP and broadcaster and chair of governors of a primary school. His new book, Medicine Balls, is published by Black and White Publishing (pound;9.99, paperback).